Ore depositional process in the Navan Zn-Pb deposit, Ireland

Zn, Fe and S isotope fractionation in a large hydrothermal system

“…In almost continuous 92 production since 1977, and currently the largest zinc producer in Europe, the ore already 93 extracted at Navan plus reserves together amount to more than 105 million tonnes at an 94 average grade of ~8.3 % zinc and ~2.1% lead (Ashton et al, 1986(Ashton et al, , 2003 The Lower Carboniferous succession (Philcox, 1984;Strogen et al, 1996) has been 108 ascribed to a northerly marine transgression. The Courceyan Navan Group comprises thin 109 red beds which pass upwards into a varied sequence of locally dolomitised, shallow marine 110 carbonates, with lesser amounts of sandstone and shale (Anderson et al, 1998). The ore 111 deposit is hosted primarily in the Pale Beds which dominate the Courceyan sequence in the 112 mine, and which comprise pale to medium grey micrites, oolitic and bioclastic calcarenites, 113 dolomite, calcareous sandstones and minor shale-silt layers.…”

“…The ore 111 deposit is hosted primarily in the Pale Beds which dominate the Courceyan sequence in the 112 mine, and which comprise pale to medium grey micrites, oolitic and bioclastic calcarenites, 113 dolomite, calcareous sandstones and minor shale-silt layers. The main orebody at Navan 114 consists of a stacked series of stratabound lenses divided into several zones by major NE to 115 ENE-trending faults (Anderson et al, 1998;Ashton et al, 2003). The Pale Beds are 116 overlain successively by the Courceyan Shaley Pales, which also contain economic 117 mineralisation, and the Courceyan to Chadian Argillaceous Bioclastic Limestones and 118…”

“…The correlation between these analyses (as 437 illustrated in Figs 6 and 7) was achieved on petrographic grounds (mainly on colour) and/or 438 by measuring the distance in relation to the layered-structure between the laser and 439 microdrilled trenches. Barite contamination was not noted during laser S analyses, and due 440 to the translucence of barite in the wavelength of the Nd-YAG laser, combustion of this 441 mineral is unlikely (Alonso-Azcárate et al, 1999); such contamination would result in 442 higher δ 34 S results since Navan barite typically has a δ 34 S >20‰ (Anderson et al, 1998 (Fig. 6b).…”

Lower Carboniferous peritidal carbonates and associated evaporites adjacent to the Leinster Massif, southeast Irish Midlands

“…The transgression resulted in deposition of extensive ramp deposits of thin bioclastic limestones, siltstones and calcareous shales (Lower Limestone Shale). Evaporites were also deposited during the Lower Courceyan in the northwest part of the Dublin Basin (North Midlands Province) and central Ireland (Philcox 1984;Phillips and Sevastopulo 1986), in the successions at Silvermines (Boyce 1990) and at Navan (Ashton et al 1986;Rizzi and Braithwaite 1996;Anderson et al 1998). The succeeding well-bedded, argillaceous limestones were deposited on the outer ramp during the proceeding transgression (Ballysteen Formation).…”

Depósitos de Pb-Zn-Cu-Ba-F-Sr epigenéticos estratoligados en series sedimentarias en relación con salmueras de cuenca: depósitos de tipo “Mississippi Valley” (MVT) y similares en México

“…Existen evidencias que apuntan a ambos lados y que, por tanto, provocan una fuerte controversia a la hora de determinar el tiempo de formación de estos depósitos. En general, la mayor parte de los depósitos se formaron por debajo del lecho marino (Navan, Anderson et al, 1998) a favor de fallas normales que actuaron como conductos de alimentación de los cuerpos masivos, y que cortaron los depósitos de la Old Red Sandstone, de edad Devónica, descargando los fl uidos en los carbonatos del Carbonífero basal. No obstante, se han encontrado evidencias de formación de algunos depósitos sobre el lecho marino (Tynagh, Silvermines y Ballynoe) como consecuencia de la descarga de los fl uidos mineralizantes a favor de fracturas que cortaron toda la serie, dando origen a chimeneas de descarga hidrotermal con su fauna típica conservada constituida por gusanos tubulares piritizados y tapices bacterianos hematitizados (Larter et al, 1981;Banks, 1985;Boyce et al, 2003).…”